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Unformatted text preview: Chapter 9 Angular Kinematics Objectives 1. Distinguish between linear, angular, and general motion. 2. Determine relative and absolute angles. 3. Discuss the relationship among the kinematic quantities of angular distance and displacement, angular velocity, and angular acceleration. 4. Discuss the conventions for the calculation of lower extremity angles. 5. Discuss the relationship between angular and linear motion, particularly displacement, velocity, and acceleration. 6. Discuss selected research studies that have used an angular kinematic approach. 7. Solve quantitative problems that employ angular kinematic principles. Angular Kinematics Angular motion: all parts of a body move through the same angle Angular kinematics deals with angular motion. Nearly all human movement involves rotation of body segments. Angular Kinematics FIGURE 9-1 A bicycle wheel as an example of rotational motion. Points A, B, and C undergo the same amount of rotation but different linear displacements, with C undergoing the greatest linear displacement. Angular Kinematics FIGURE 9-2 A gymnast completing a cartwheel as an example of general motion. The gymnast simultaneously undergoes both translation and rotation. Measurement of Angles Angle FIGURE 9-3 Components of an angle. Note that the lines are usually segments and the vertex of the angle is the joint center. With machines, the center of rotation is usually fixed. This is not the case with human joint. Measurement of Angles Angle FIGURE 9-4 Instantaneous center of rotation of the knee.. An angle is at the intersection of two lines (and planes). Units of measurement Degrees Radians (1 radian = 57.3 o most commonly used), Revolutions (one revolution = 360 o ) One radian is the angle at the center of a circle described by an arc equal to the length of the radius. Circumference = 2 r; therefore, there are 2 radians in 360 o Measurement of Angles Units of Measurement FIGURE 9-5 Units of angular measurement. A.Revolution; B.Perpendicular and straight lines; C.Radian. Measurement of Angles Units of Measurement A. B. C. An absolute angle is measured from an external frame of reference. The most usual convention is to measure the angle anticlockwise from the right horizontal Types of Angles Absolute Angles Types of Angles Absolute Angles FIGURE 9-6 Absolute angles: The arm (a), trunk (b), thigh (c), and leg (d) of a runner. Types of Angles Absolute Angles FIGURE 9-7 Absolute angles of the thigh and leg as defined in a coordinate system. Types of Angles Absolute Angles FIGURE 9-8 To calculate absolute angles relative to the right horizontal requires adjustments when the orientation is such that the differences between the proximal and distal end points indicate that the segment is not in the first quadrant. Types of Angles...
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